In the environmental clean-up of government facilities, one important aspect is the sampling of potentially contaminated soil. A considerable amount of work has been done taking soil samples, dissolving them in various organic and aqueous solvents, and analyzing the solvates. The solvates may contain constituents as diverse as viscous hydrocarbons, toxic chemicals, or nuclear waste. The soil samples themselves may consist of fine sands, chunks of various solids, some very abrasive or sharp, and liquids of unknown character.
When confronted with the need to rapidly prepare, filter and analyze many such environmental soil samples, various commercial devices were investigated. A representative, commercially available filter system of standard design is shown schematically in FIG. 1.
Referring to FIG. 1, canister 2 contains solids 4 from liquid 6 to be filtered. O-ring 8 forms a slideable sealing arrangement between inner walls 10 of canister 2 and pneumatic piston 12. Filter element 14 is located adjacent canister lid 16. O-rings 18 and 20 form a seal between lid 16 and filter element ring 22 which secures the filter element 14 in position.
To separate solids 4 from liquid 6, pressurized air 24 is delivered through inlet port 26. The air moves piston 12 and forces liquid 6 and any gases through outlet 28 in lid 16.
While the above-described apparatus is fairly effective at separating solids 4 from liquid 6, it is very difficult and time consuming to clean. Leakage around O-ring 8 was common, resulting in liquids contaminating the area around inlet port 26. Furthermore, piston 12 tended to get stuck in canister 2 and often had to be pounded out for cleaning. Difficulty disassembling the unit also tended to damage O-rings and seals, requiring at least partial replacement every cycle or risking potential leaks. These problems led to long turnaround times between processing samples. They also made the risk of cross-contamination of samples much greater.
Accordingly, there has been a long felt need for a fast, efficient, sanitary and easily cleaned filtering apparatus.